If you have an ipad already & have two weeks until you get the new iPad, why not download the apps & try using them. If your current iPad is smaller than 10", you can use the apps for free. I used them for my MBA & found them to be quite good, but not good enough to completely eliminate the need for a computer. Everything sracer said above is completely true. Of the three, I found Excel to be the most frustrating to use on the iPad, Powerpoint the best & word in the middle.
As far as which set to go with, Office or iWork, if you are going to be sharing files with others who use office, I'd recommend using the office apps. If the work you will be doing will only be shared as PDF's or you will be doing presentations using the iPad, then iWork becomes more of an option. Numbers however, is much more limited than Excel, and some of those limitations would drive me nuts after a while. Also, which ever one you go with, I would recommend downloading & keeping both on your iPad for a couple of reasons.
1. Each app has it's strengths. I find Pages to be much easier to add pictures, etc to documents, but the Office apps can't be beat for compatibility with the outside world. Often times I would create a document in Pages/ Numbers, and then export it to Word/ Excel, and finish it off in there so I could send it out and guarantee compatibility.
2. There were times when I needed to view one document and work on another at the same time (two word docs or two excel spreadsheets). There is no practical way to do this with an iPad using only one app (there may be some new way that I'm not aware of, but when I did this extensively two years ago, there wasn't). Each app can open only one doc at a time, so I would open the one I wanted to read in one app & the one I wanted to work on in the other (Pages & Word or Numbers & Excel), and you can then use Split screen to access both at the same time. (When I was doing it, you had to do the 4 finger swipe to go between docs).
Good luck on your adventure. open piece of advice I would offer is that it gets easier as you go along. Using office apps on an iPad will never be as easy as working on a computer, but as you get used to how the apps work, you get much faster on them, and they become much easier/more enjoyable to use.